gh-36177: fix and activate pycodestyle E305 in py files
fix and activate
- pycodestyle E305 in py files
- pycodestyle E502 in pyx file (one fix only)
### :memo: Checklist
- [x] The title is concise, informative, and self-explanatory.
- [x] The description explains in detail what this PR is about.
URL: https://github.com/sagemath/sage/pull/36177
Reported by: Frédéric Chapoton
Reviewer(s): David Coudert, Tobias Diez
